A typical photographic material processing method comprises developing the photographic material by treatment with a developer, and fixing the developed photographic material by treatment with a fixer. During the fixing step, the non-developed silver halide is removed from the photographic material and silver ions build up in the fixer, having the effect of slowing down the fixing process. It is therefore not unusual to reduce the level of silver ions in the fixer by electrolysis, for example by passing the fixer around a circulation loop which includes an electrolytic cell. Electrolytic removal of silver also has the benefit of enabling a lower regeneration rate of fixer to be used and this is consistent with recent trends to reduce the volume of treatment liquids used in photographic processing.
In such a process the photographic material which passes from the developer to the fixer carries with it a certain amount of developer liquid, containing used and unused developing agents and other components, which act as contaminants to the fixer. The consequence of this "carry-over" is that the time required for the photographic material to be fixed in the fixer, i.e. for the silver ion content of the photographic material to be reduced to a predetermined low level, is lengthened. The greater the degree of carry-over, the longer is the required fixing time. While improved apparatus design, such as the design of transport rollers used to feed the photographic material through the apparatus, can reduce the level of carry-over, it has not so far been possible to totally eliminate carry-over, and the corresponding time-loss in the fixing step.
While it has been proposed to rinse the photographic material with water or a rinse liquid between the developer and the fixer, to wash off carried-over developer and thus reduce the increase in fixing time which the carried-over developer would cause, the time taken for such rinsing becomes a factor in the overall processing time, so that any benefits obtained from more efficient fixing are not wholly realised. Furthermore, there is a trend towards processes which consume lower amounts of water. One disadvantage of rinsing with water between the developer and fixer is the production of an additional waste stream. Moreover, an undesired brownish discolouration may arise from oxidation of developer components, which may foul the photographic material. This discolouration is particularly severe when low levels of rinse water are used in order to limit the additional waste. Another disadvantage is the additional time necessary, which is wasted time as this time is not used for processing.
In general, the efficiency of fixing can be improved by the use of "cascade" fixing, in which the photographic material passes through two fixing vessels, the fixer moving counter-current to the photographic material. The period of time spent by the photographic material in the fixer is thereby increased while the volume of fixer required to fill the processing apparatus is increased.